C.5 Geology, Soils, and Paleontology...Andreas Fault Zone are several members of the Anaverde...

Antelope-Pardee 500-kV Transmission Project C.5 GEOLOGY, SOILS, and PALEONTOLGY

Final EIR/EIS C.5-1 December 2006

C.5 Geology, Soils, and Paleontology This section addresses the environmental setting and impacts related to the construction and operation of the

proposed Project and alternatives involving the issues of geologic and seismic hazards, and paleontology. The

primary reason to define geologic and seismic hazards is to protect structures from physical damage and to

minimize injury/death of people due to structure damage or collapse. Section C.5.1 provides a summary of

existing geological, soil, and paleontological conditions present along the alignment of SCE’s Antelope-Pardee

500-kV Transmission Project and associated geologic and seismic hazards. Applicable regulations, plans, and

standards are listed in Section C.5.2. Potential impacts and mitigation measures for the proposed Project are

presented in C.5.5; and alternatives are discussed in Sections C.5.6 through C.5.11.

C.5.1 Affected Environment

Baseline geologic, seismic, soils, and paleontological information were collected from published and

unpublished literature, GIS data, and online sources for the proposed Project and the surrounding area. The

literature and data review was supplemented by a brief field reconnaissance of the proposed alignment. The

literature review and field reconnaissance focused on the identification of specific geologic hazards and

paleontologic resources.

C.5.1.1 Physiography

The Antelope-Pardee 500-kV Transmission Project is located within the Transverse Ranges geomorphic

province of southern California, which is characterized by a complex series of mountain ranges and valleys with

dominant east-west trends. The Antelope-Pardee Project traverses four distinct geographic areas, the Antelope

Valley, the Leona Valley (the San Andreas Rift Zone), the Liebre-Sierra Pelona Mountains, and the Santa

Clarita Valley. The Antelope Valley consists of approximately 1200 square miles of elevated desert terrain,

located along the western edge of the Mojave Desert. The Leona Valley is a small, northwest-southeast trending

longitudinal valley formed by movement on multiple overlapping strands of the San Andreas Fault in the San

Andreas Rift Zone, and in the Project area is bounded on the northeast by the Portal Hills and on the southwest

by foothills of the Sierra Pelona. The Liebre-Sierra Pelona Mountains are a small northwest-southeast trending

mountain range within the central Transverse Ranges. The Santa Clarita Valley is primarily formed by the

convergence of the Santa Clara River with several large unnamed streams that flow from the north from Castaic

Valley and, San Francisquito, Dry, and Bouquet Canyons. Additionally, lateral fault movement of the San

Gabriel Fault has caused the Santa Clarita Valley to be offset and widened in the Project area.

Elevations along the proposed alignment range from about 1060 feet at the Pardee Substation to approximately

4,200 feet above mean sea level (msl) in the Liebre-Sierra Pelona Mountains near where the alignment crosses

the Grass Mountain Leona Divide Road. The Antelope Substation is located at an elevation approximately 2470

feet above msl. Elevations were determined using USGS 7½ minute quadrangles from 3-D TopoQuads software

(Delorme, 1999).

Antelope-Pardee 500-kV Transmission Project C.5 GEOLOGY, SOILS, and PALEONTOLOGY

December 2006 C.5-2 Final EIR/EIS

C.5.1.2 Geologic Conditions and Hazards

Geologic Setting

The Antelope-Pardee transmission line would cross four areas of distinctive geologic character and province,

the Antelope Valley, the San Andreas Rift Zone, the Liebre-Sierra Pelona Mountains, and the Soledad Basin.

The regional geology of the Project area is depicted on Figure C.5-1.

Antelope Valley. The Antelope Valley is primarily an alluviated desert plain containing bedrock hills and low

mountains. The rocks of the western Antelope Valley are characterized by relatively flat-lying topography and

valley fill deposits. In the Project area and vicinity, the western Antelope Valley is covered primarily by alluvial

deposits of Quaternary age: Holocene Alluvium and Pleistocene Older Alluvium. The Holocene alluvial

deposits consist of slightly dissected alluvial fan deposits of gravel, sand and clay. The Older Alluvium is

located primarily near the margins of the Antelope Valley at the flanks of Portal Ridge and consists of weakly

consolidated, uplifted and moderately to severely dissected alluvial fan and terrace deposits composed primarily

of sand and gravel (Dibblee, 2002). The ridges are comprised of crystalline rocks of igneous and metamorphic

composition. The west-trending Hitchbrook Fault, which diverges from the San Andreas Fault northwest of the

Project area, separates Portal Ridge, with Pelona Schist on the southeast from granitic rocks on the northwest.

Beyond the ridge, the Project alignment crosses into the San Andreas rift zone in Leona Valley.

San Andreas Rift Zone. In the Project area, the San Andreas Fault lies within a linear, trough-like valley

called the San Andreas Rift Zone. The Rift Zone in the Project area consists of several anastomosing fault

segments (i.e. interlacing faults), which along with the presence of Amargosa Creek, has widened the zone into

a valley, the Leona Valley. Holocene Alluvium, Pleistocene Older Alluvium, and the non-marine Pliocene

Anaverde Formation underlie the Lenore Valley. Exposed among interlacing fault strands within the San

Andreas Fault Zone are several members of the Anaverde Formation: the sandstone, clay shale, and breccia

members (CGS, 2006; Dibblee, 2002). The sandstone member is a medium-to thick-bedded, locally massive,

fine to coarse-grained, locally pebbly, with local thin silty interbeds. The clay shale member is a thin-bedded,

sandy, silty, locally very gypsiferous clay shale with interbedded siltstone and sandstone layers. The breccia

member is a distinctive, reddish to dark gray, massive, pervasively sheared sedimentary breccia with angular

clasts of hornblende diorite. The bedding within the Anaverde Formation members mostly parallel the bounding

faults, and has steep to vertical dips (CGS, 2006).

Liebre-Sierra Pelona Mountains. The Liebre-Sierra Pelona Mountains are composed of late Mesozoic or older

granitic and metamorphic rocks north of the Clearwater Fault, Paleocene (early Tertiary) San Francisquito

Formation between the Clearwater and San Francisquito Faults, and Mesozoic or older Pelona Schist south of

the San Francisquito Fault. The granitic and metamorphic rocks consist of a complex mixture of biotite rich,

closely fractured quartz diorite and gneiss with local inclusions of diorite and amphibolite. San Francisquito

Formation is a layered marine clastic, lithified sedimentary rock formation comprised of thick-bedded arkosic

sandstone, cobble and pebble conglomerate, and clay shale and siltstone. The Pelona Schist is primarily

composed of distinctive bluish gray schist that was metamorphosed from clastic and pryoclastic sedimentary

rocks.

Soledad Basin. The Soledad depositional basin is juxtaposed against the Ventura depositional along the San

Gabriel Fault, a major structural boundary feature. Rocks that accumulated in the Soledad Basin are exposed

northeast of the fault. Geologic units exposed within Project area consist of upper Miocene Mint Canyon

Formation, upper Miocene Castaic Formation, Plio-Pleistocene Saugus Formation, Pleistocene Older Alluvium,



and Holocene Alluvium. The nonmarine Mint Canyon Formation consists of well-bedded interlayered

conglomeratic sandstone, claystone, and siltstone of fluvial and lacustrine origin. Overlying the Mint Canyon

Formation is the Castaic Formation which consists of shallow marine sandstone and shale, distinguishable by

the large variety of mollusk species from the upper Miocene. The Saugus Formation, which is the dominant

rock unit exposed in the area is composed of interbedded nonmarine sandstone, siltstone, and pebble-cobble

conglomerate. The Older Alluvium consists of subunits of older alluvial fans and older terrace deposits of

poorly consolidated interbeds of sand, silt, and gravel. Alluvium covers the floor and margins of the valley

formed by the Santa Clara River and extend up into the canyons in the surrounding hills and mountains. The

Alluvium consists of slope wash, landslide deposits, and younger alluvium. Modern man-made fill is also

mapped in some areas.

Project Geologic Conditions. Geologic conditions likely to be encountered during construction of the proposed

Antelope-Pardee 500-kV Transmission Project are summarized in Table C.5-1. The table includes: name of the

geologic formation or feature; the geologic age of the formation or feature, a description and comments about

the formation’s general rock type, lithology, and susceptibility to specific geologic hazards as appropriate; and

general excavation characteristics of the unit related to excavation or drilling of tower and structure foundations.

Descriptions of geologic units in the Project area are based on published geologic quadrangle maps by Thomas

Dibblee (1996b, c; 1997a, b; 2002).

Table C.5-1. Geology along the Proposed Antelope-Pardee 500-kV Transmission Line Route

Mile Marker1, 2

Formation/ Feature Name1

Geologic Age of Formation/ Feature

Description/Comments1 Excavation

Characteristics3

Antelope Valley and Foothills 0 -2.3 Alluvium Holocene Antelope Substation at MP 0; Alluvial sand and clay Easy 2.3 – 2.8 Older Alluvium Pleistocene Sand and gravel fan deposits Easy

2.8 – 3.0 Quartz

monzonite Cretaceous Granitic rocks, variable weathering profile Difficult

3.0 – 3.4 Alluvium Holocene Identified liquefaction potential Easy

3.2 Hitchbrook Fault

Holocene Branch fault of the San Andreas Fault Zone; minor fault rupture hazard, this branch not currently considered active

Not Applicable

3.4-3.8 Pelona Schist Unknown, assumed late Miocene or older

Mica schist of Portal Ridge, Identified landslide potential Difficult

San Andreas Rift Zone 3.8 -4.3 Alluvium Holocene Identified liquefaction potential Easy

4.3-4.7

San Andreas Fault Rift Zone and Anaverde

Fm

Recent and Holocene

Pliocene

Rift zone of San Andreas Fault; significant fault rupture hazard Anaverde Formation (sandstone, shale, and breccia) and quartz diorite; identified landslide hazard potential

Easy

4.7-5.2 Alluvium Holocene Identified liquefaction potential Easy

5.1 San Andreas

Fault Recent & Holocene

Concealed strand of the San Andreas Fault Not Applicable

Liebre Mountain - Sierra Pelona Uplift

5.2-9.4 Quartz diorite Late Mesozoic and older

Granitic rocks, variable weathering profile, possible landslide hazard potential

Difficult

9.4 Clearwater Fault

Late Quaternary Potentially active, minor rupture hazard Not Applicable

9.4-10.5 San

Francisquito Fm

Paleocene Lithified, fractured, marine clastic rocks. Argillaceous shales and sandstones; possible landslide hazard potential

Moderate to Difficult

10.5 San

Francisquito Fault

Pre-Quaternary Likely inactive, no significant fault rupture hazard Not Applicable



Table C.5-1. Geology along the Proposed Antelope-Pardee 500-kV Transmission Line Route

Mile Marker1, 2

Formation/ Feature Name1

Geologic Age of Formation/ Feature

Description/Comments1 Excavation

Characteristics3

10.5-12.3.3

Pelona Schist Unknown, assumed late Miocene or older

Mica schist, out-of-slope dipping foliation; landslide hazard potential

Difficult

12.3-12.8 Landslide Recent Large feature in foliated metamorphic rock; Difficult



Difficult

13.1-13.8 Landslide Recent Large feature in foliated metamorphic rock; landslide hazard potential

Difficult



Difficult

Soledad Basin

17.5-19.8 Mint Canyon

Fm middle Miocene

Moderately indurated terrestrial fluviatile, predominantly sandstone; identified landslide hazard potential; liquefaction potential in alluvial areas

Moderate

19.8-20.5 Castaic Fm late Miocene Clastic marine sediments, claystone w/ lesser sandstone; identified landslide hazard potential

Moderate

20.5-20.6 Alluvium Holocene Haskell Canyon; identified liquefaction potential Easy

20.6-22.8 Saugus Fm Pliocene/ Pleistocene

Weakly indurated, terrestrial fluviatile conglomerate; identified landslide hazard potential

Easy to Moderate

22.8-22.9 Alluvium Holocene Dry Canyon, identified liquefaction potential



Easy to Moderate

23.8-24.1 Alluvium Holocene Sand and gravel in San Francisquito Canyon; identified liquefaction potential

Easy


Weakly indurated, terrestrial fluviatile conglomerate; identified seismically induced landslide hazard potential

Easy to Moderate

25.1 San Gabriel Fault

Holocene Active right slip fault; fault rupture hazard Not Applicable

25.1-25.2 Alluvium Holocene Reentrant off Santa Clara River Valley, identified liquefaction potential

Easy



Easy to Moderate

25.3-25.6 Alluvium Holocene Sand and gravel, Santa Clara River Valley; identified liquefaction potential; Pardee Substation at mile 25.6

Easy

Notes: 1) Information in these columns is primarily derived from Table 4.7-1 of the PEA. Project milepost measurements were assumed to be accurate and not remeasured.

2) Refer to Figure C.5-1 (Regional Geologic Map) for approximate mile marker locations, actual mileposts (from PEA) for the alignment measured from geology on Dibblee geologic maps.

3) Excavation characteristics are very generally defined as “easy,” “moderate,” or “difficult” based on increasing hardness of the rock unit. Excavation characteristic descriptions are general in nature and the actual ease of excavation may vary widely depending on site-specific subsurface conditions.

Previous Geotechnical Studies

Reports and memos for various geotechnical investigations that have been conducted at both the Antelope and

Pardee Substations were reviewed and are listed below.

Antelope Substation

• Letter Report: Antelope Substation – Pile Design Data; T.M. Leps, Chief Civil Engineer, April 25, 1952

• Memorandum: Antelope Substation, Foundation Investigation; E.E. Chandler, Assistant Civil Engineer, July 19, 1957

• Antelope Substation Boring Logs and Soil Test Results; December 1996



• Letter Report: Foundation Design Recommendations, Antelope Substation Additions, Los Angeles County, California; Engineering and Technical Services Geotechnical Group, January 9, 1997

The reports and data reviewed for the Antelope Substation indicate that the materials underlying the site consist

of Recent Alluvium, composed primarily of loose to medium dense silty sand with gravel, with local gravelly,

cobbly, and clayey layers. No groundwater was encountered in any of the borings conducted for these

investigations; the borings were conducted to a maximum depth of 40 feet.

Pardee Substation

• Report of Geotechnical Investigation, Pardee Substation Site, Near Castaic Junction, California; for Southern California Edison Company; Evans, Goffman & McCormick, May 15, 1970

• Report of Inspection and Testing of Site Grading, Pardee Substation, County of Los Angeles; for Southern California Edison; Evans, Goffman & McCormick, August 26, 1970

• Pardee Substation: Portal Structure Foundation Void Grouting; Edison Geotechnical Group, June 24, 1994

Review of the above listed reports for the Pardee Substation indicate that the site is underlain by Recent to

Older Alluvium ranging from relatively firm, dense sand and silty sand in the northeastern portion of the site to

very soft clayey to sandy silt in the southern portion of the site. Groundwater is relatively shallow beneath the

site and was encountered at depths of 9 to 12 feet below ground surface. During construction of the facility,

grading was conducted consisting of excavation and cut of sloping hillside areas at the northeastern portion of

the property and fill in the center of the property. Minor cut and fill was also conducted in other areas of the

site during grading for facility construction.

The 1994 Northridge Earthquake caused severe groundshaking at the Pardee Substation, resulting in shaking

and rocking of the portal towers. This rocking motion resulted in the tower footings moving within the

surrounding soil and created voids between the concrete piles and the soil. Pressure grouting was conducted at

22 tower locations to fill the voids in the soil and return the soil to pre-earthquake strength; one tower was

replaced due to severe damage to the tower and footing.

Slope Stability

Important factors that affect the slope stability of an area include the steepness of the slope, the relative strength

of the underlying rock material, and the thickness and cohesion of the overlying colluvium. The steeper the

slope and/or the less strong the rock, the more likely the area is susceptible to landslides. The steeper the slope

and the thicker the colluvium, the more likely the area is susceptible to debris flows. Such areas can be

identified on maps showing the steepness of slopes (Graham and Pike, 1998) when used in combination with a

geologic map. Another indication of unstable slopes is the presence of old or recent landslides or debris flows.

Most of the proposed alignment and the alternatives do not cross any areas identified as an existing landslide,

except along Del Sur Ridge where the alignment passes across two mapped landslides in the Pelona Schist.

However, although not crossed by the Project alignment, other landslides have been mapped in the Project

vicinity within several of the geologic units traversed by the Project alignment: the Pelona Schist, the Mint

Canyon Formation, the Castaic Formation, and the Saugus Formation (Dibblee, 1996b, 1996c, 1997a and

1997b). Unmapped landslides and areas of localized slope instability may be encountered in the hills traversed

by the proposed Project alignment.

Soils

The soils along the proposed transmission line route reflect the underlying rock type, the extent of weathering of

the rock, the degree of slope, and the degree of modification by man. Much of the route south of the ANF goes



through developed land, while the portion traversing the ANF passes through undeveloped open space and the

route north of ANF traverses a mixture of agricultural and undeveloped land. Soil mapping by the USDA

National Resource Conservation Service (NRCS) has provided information for surface and near-surface

subsurface soil materials. The Project alignment traverses portions of two NRCS soil survey reports, the Soil

Survey of Antelope Valley, California (1970) and the Soil Survey of the Angeles National Forest Area,

California (1980). A summary of the significant characteristics of the major soil units traversed by the Project is

presented in Table C.5-2. These soil units are presented in approximate order of first significant occurrence

along each portion of the alignment, each unit may occur numerous times and at several locations along the

alignment.

Table C.5-2. Major Soils along the Proposed Antelope-Pardee 500-kV Transmission Line Route

Risk of Corrosion

Soil Name Description

Hazard of Erosion on Roads and Trails1,2

Uncoated Steel Concrete

North of ANF (Mile 0 to 5.7)

Greenfield Sandy Loam on 2-9 percent slopes Moderate Low Low Ramona Coarse sandy loam on 2-5 and 5-9 percent slopes;

and sandy loam on 9 to 30 percent slopes Moderate to Severe

Moderate Moderate

Greenfield Sandy Loam on 2-9 percent slopes Moderate Low Low Vista Coarse sandy loam on 15-30 and 30-50 percent

slopes Severe Low Low

Hanford Coarse sandy loam and gravelly sandy loam on 2 to 9 percent slopes

Moderate Low Low

Vista Coarse sandy loam on 15-30 and 30-50 percent slopes

Severe Low Low

Amargosa Rocky coarse sandy loam on 9-55 percent slopes Severe Moderate Low Angeles National Forest (Mile 5.7 to 18.6)

Trigo-Exchequer Gravelly sandy loam, sandy loam, and loam on 30 to 60 and 60 to 100 percent slopes

Severe NA NA

Stonyford-Milsholm Gravelly clay loam and clay loam on 30 to 70 percent slopes.

Severe NA NA

Lodo-Modesto Gravelly loam with some loam and clay loam on 30 to 70 percent slopes

Severe NA NA

Calcixerollic Xerochrepts-Calleguas

Clay loam with some silty loam on 30 to 60 percent slopes

Severe NA NA

Trigo-Exchequer Gravelly sandy loam, sandy loam, and loam on 30 to 60 and 60 to 100 percent slopes

Severe NA NA

South of ANF (Mile 18.6 to 25.6)

Hanford Sandy loam on 0-2 and 2-9 percent slopes Slight to Moderate

Low Low

Metz Loam on 2-5 percent slopes; and loamy sand on 2-9 percent slopes

Moderate High Low

Saugus Loam on 30-50 percent slopes Severe Low Low NA – data not available

1) Data related to hazard of erosion on roads and trails from the Hazard of Erosion and Suitability for Roads on ForestlandTable from the USDA NRCS online tabular data for the Antelope Valley (data version 1, 3/2004) and Angeles National Forest Area (data version 1, 12/2004) soil surveys. Erosion Hazard: Slight – little or no erosion is likely, Moderate – some erosion is likely and that simple erosion control measures are needed, Severe – significant erosion is expected and major erosion control measures may be needed.Erosion Hazard: Slight – little or no erosion is likely, Moderate – some erosion is likely and that simple erosion control measures are needed, Severe – significant erosion is expected and major erosion control measures may be needed.

Corrosivity of soils is generally related to several key parameters: soil resistivity, presence of chlorides and

sulfates, oxygen content, and pH. Typically, the most corrosive soils are those with the lowest pH and highest

concentration of chlorides and sulfates. High sulfate soils are corrosive to concrete and may prevent complete



curing reducing its strength considerably. Low pH and/or low resistivity soils could corrode buried or partially

buried metal structures.

The properties of soil which influence erosion by rainfall and runoff are ones which affect the infiltration

capacity of a soil and those which affect the resistance of a soil to detachment and being carried away by falling

or flowing water. Soils containing high percentages of fine sands and silt and that may have be low in density

are generally the most erodible. These soil types generally coincide with soils such as young alluvium and other

surficial deposits (Dibblee 1996b, c; 1997a, b; 2002), which likely occur in areas throughout the Project area.

As the clay and organic matter content of these soils increases, the potential for erosion decreases. Clays act as

a binder to soil particles, thus reducing the potential for erosion. However, while clays have a tendency to resist

erosion, once eroded they are easily transported by water. Clean, well-drained, and well-graded gravels and

gravel-sand mixtures are usually the least erodible soils. Soils with high infiltration rates and permeabilities

reduce the amount of runoff.

Expansive soils are characterized by their ability to undergo significant volume change (shrink and swell) due to

variation in soil moisture content. Changes in soil moisture could result from rainfall, landscape irrigation,

utility leakage, roof drainage, and/or perched groundwater. Expansive soils are typically very fine grained with

a high to very high percentage of clay.

Mineral Resources

The Project traverses areas identified as sand and gravel resources by the State Mining and Geology Board in

the Santa Clara River valley, however no active production/quarrying operations are located near the Project

(CDMG 1987, 1999). The Project alignment does cross very near to one active quarry site, between Miles 13

and 14, off of Del Sur Ridge Road, the Bouquet Canyon Stone Quarry. The quarry is owned by Bouquet

Canyon Stone Co., Inc. and is currently in operation mining rock used for decorative stone purposes. The rock

they are mining is a sericite schist that is unique within the Pelona Schist for its variable-tone blue grey, gold

color, very flat planar surfaces and tough structural integrity (Bouquet Canyon Stone Co., Inc., 2005). No other

active mines or quarries are located in the Project vicinity.

The Pardee Substation is located adjacent to the Southeast Area of the Honor Rancho Oil and Gas Field and part

of the Project alignment crosses the southeast corner of the field (DOGGR, 2005). The Southeast Area of the

Honor Rancho field is a natural gas storage area, operated primarily by Southern California Gas Co.

(SoCalGas) (DOGGR, 2002).

C.5.1.3 Seismic Hazards

Faults and Seismicity

The seismicity of southern California is dominated by the intersection of the north-northwest trending San

Andreas Fault system and the east-west trending Transverse Ranges fault system. Both systems are responding

to strain produced by the relative motions of the Pacific and North American Tectonic Plates. This strain is

relieved by right-lateral strike-slip faulting on the San Andreas, and related faults, left-lateral strike slip on the

Garlock Fault, and by vertical, reverse-slip or left-lateral strike-slip displacement on faults in the Transverse

Ranges. The effects of this deformation include mountain building; basin development; deformation of

Quaternary marine terraces; widespread regional uplift; and generation of earthquakes. Both the Transverse

Ranges and northern Los Angeles County area are characterized by numerous geologically young faults. These

faults can be classified as historically active, active, potentially active, or inactive, based on the following

criteria (CGS, 1999):



• Faults that have generated earthquakes accompanied by surface rupture during historic time (approximately the last 200 years) and faults that exhibit aseismic fault creep1 are defined as Historically Active.

• Faults that show geologic evidence of movement within Holocene time (approximately the last 11,000 years) are defined as Active.

• Faults that show geologic evidence of movement during the Quaternary (approximately the last 1.6 million years) are defined as Potentially Active.

• Faults that show direct geologic evidence of inactivity during all of Quaternary time or longer are classified as Inactive.

Although it is difficult to quantify the probability that an earthquake will occur on a specific fault, this

classification is based on the assumption that if a fault has moved during the Holocene epoch, it is likely to

produce earthquakes in the future. Blind thrust faults do not intersect the ground surface, and thus they are not

classified as active or potentially active in the same manner as faults that are present at the earth’s surface. Blind

thrust faults are seismogenic structures and thus the activity classification of these faults is predominantly based

on historic earthquakes and microseismic activity along the fault.

Since periodic earthquakes accompanied by surface displacement can be expected to continue in the study area

through the lifetime of the proposed Project, the effects of strong groundshaking and fault rupture are of

primary concern to safe operation of the proposed transmission line and associated facilities.

The Project area will be subject to ground shaking associated with earthquakes on faults of both the San

Andreas and Transverse Ranges fault systems. Active faults of the San Andreas system are predominantly

strike-slip faults accommodating translational2 movement. The predominant active fault of the San Andreas

Fault system in the Project area is the San Andreas Fault, which has been responsible for many of the damaging

earthquakes in California in historical times.

Active reverse or thrust faults3 in the Transverse Ranges include blind thrust faults4 responsible for the 1987

Whittier Narrows Earthquake and 1994 Northridge Earthquake, and the range-front faults5 responsible for uplift

of the Santa Susana and San Gabriel Mountains. The Transverse Ranges fault system consists primarily of

blind, reverse, and thrust faults accommodating tectonic compressional stresses in the region. Blind faults have

no surface expression and have been located using subsurface geologic and geophysical methods. This

combination of translational and compressional stresses gives rise to diffuse seismicity across the region.

Figure C.5-2 shows locations of active and potentially active faults (representing possible seismic sources) and

earthquakes in the region surrounding the Project area. Active and potentially active faults within 50 miles of

the Project alignment that are significant potential seismic sources are presented in Table C.5-3.

Table C.5-3. Significant Active and Potentially Active Faults in the Project Area

Name Closest Distance

to Project (miles)1

Estimated Max. Earthquake Magnitude2, 3

Fault Type and Dip Direction3 Slip Rate (mm/yr)3, 4

San Gabriel 0.6 7.2 Right Lateral Strike Slip, 90° 1.0 Holser 0.8 6.5 Reverse, 65° S 0.4 San Andreas – Mojave Segment 4.1 7.4 Right Lateral Strike Slip, 90° 30.0

1 Movement along a fault that does not entail earthquake activity. 2 Fault block movement in which the blocks have no rotational component, parallel features remain so after movement. 3 A fault with predominantly vertical movement in which the upper block moves upward in relation to the lower block, a thrust

fault is a low angle reverse fault. 4 Blind thrust faults are low-angled subterranean faults that have no surface expression. 5 Faults along the front of mountain ranges responsible for the uplift of the mountains.



Table C.5-3. Significant Active and Potentially Active Faults in the Project Area

Name Closest Distance

to Project (miles)1

Estimated Max. Earthquake Magnitude2, 3

Fault Type and Dip Direction3 Slip Rate (mm/yr)3, 4

Northridge 6.2 7.0 Blind Thrust, 42° S 1.5 Santa Susana 6.6 6.7 Reverse, 55° N 5.0 Oak Ridge 8.5 7.0 Reverse, 65° S 4.0 Sierra Madre 9.0 6.7 Reverse, 45° S 2.0 Simi-Santa Rosa 10.2 7.0 Left Lateral Reverse Oblique, 60° N 1.0 San Cayetano 10.2 7.0 Reverse, 60° N 6.0 San Andreas – Carrizo Segment 11.7 7.4 Right Lateral Strike Slip, 90° 34.0 Verdugo 15.1 6.9 Reverse, 45° NE 0.5 Santa Ynez 20.8 7.1 Left Lateral Strike Slip, 90° 2.0 Garlock 23.5 7.3 Left Lateral Strike Slip, 90° 6.0 Hollywood 24.9 6.4 Left Lateral Reverse Oblique, 70° N 1.0 Anacapa-Dume 26.0 7.5 Reverse Left Lateral Oblique, 45° N 3.0 Upper Elysian Park Thrust 26.2 6.4 Blind Thrust, 50° NE 1.3 Santa Monica 26.3 6.6 Left Lateral Reverse Oblique, 75° N 1.0 Malibu Coast 26.8 6.7 Left Lateral Reverse Oblique, 75° N 0.3 Raymond 29.5 6.5 Left Lateral Reverse Oblique, 75° N 1.5 Newport-Inglewood 29.8 7.1 Right Lateral Strike Slip, 90° 1.0 Puente Hills Blind Thrust 29.9 7.1 Blind Thrust, 25° N 0.7 Clamshell-Sawpit 31.8 6.5 Reverse, 45° NW 0.5 Ventura-Pitas Point 32.5 6.9 Reverse Left Lateral Oblique, 75° N 1.0 Plieto 33.1 7.0 Reverse, 45° S 2.0 Palos Verdes 34.0 7.3 Right Lateral Strike Slip, 90° 3.0 Big Pine 35.7 6.9 Left Lateral Strike Slip, 90° 0.8 White Wolf 38.3 7.3 Reverse Left Lateral Oblique, 60° S 2.0 Whittier 45.0 6.8 Right Lateral Strike Slip, 90° 2.5 Cucamonga 47.3 6.9 Reverse, 45° N 5.0 San Jose 47.5 6.4 Left Lateral Reverse Oblique, 75° NW 0.5 Lenwood-Lockhart-Old Woman Springs

48.0 7.5 Right Lateral Strike Slip, 90° 0.6

Notes: 1) Fault distances obtained using the EQFault computer program (Blake, 2000), based on digitized data adapted and modified from the 2002 CGS fault database.

2) Maximum Earthquake Magnitude – the maximum earthquake that appears capable of occurring under the presently known tectonic framework, using the Richter scale.

3) Fault parameters from the CGS Revised 2002 California Probabilistic Seismic Hazard Maps report, Appendix A - 2002 California Fault Parameters.

4) References to fault slip rates are traditionally presented in millimeters per year.

Strong Groundshaking

An earthquake is classified by the amount of energy released, which traditionally has been quantified using the

Richter scale. Recently, seismologists have begun using a Moment Magnitude (M) scale because it provides a

more accurate measurement of the size of major and great earthquakes. For earthquakes of less than M 7.0, the

Moment and Richter Magnitude scales are nearly identical. For earthquake magnitudes greater than M 7.0,

readings on the Moment Magnitude scale are slightly greater than a corresponding Richter Magnitude.



The intensity of the seismic shaking, or strong ground motion, during an earthquake is dependent on the

distance between the Project area and the epicenter of the earthquake, the magnitude of the earthquake, and the

geologic conditions underlying and surrounding the Project area. Earthquakes occurring on faults closest to the

Project area would most likely generate the largest ground motion.

The intensity of earthquake induced ground motions can be described using peak site accelerations, represented

as a fraction of the acceleration of gravity (g). GIS data based on the CGS Probabilistic Seismic Hazard

Assessment (PSHA) Maps was used to estimate peak ground accelerations along the Project alignment. PSHA

Maps depict peak ground accelerations with a 10 percent probability of exceedance in 50 years. The results for

the proposed Project are presented in Table C.5 4.

Table C.5-4. Peak Ground Acceleration

Approximate Proposed Transmission Line Mile

Total Length of Segments (miles)

Peak Ground Acceleration

15.1 to 20.5 5.4 0.4 to 0.5g

0 to 1.6, 10.8 to 15.1, and 20.5 to 25.2 10.6 0.5 to 0.6g

1.6 to 3.9, 7.8 to 10.8 and 25.2 to 25.6 5.7 0.6 to 0.7g

3.9 to 7.8 3.9 0.7 to 0.8g

A review of historic earthquake activity from 1800 to 1999 indicates that eight earthquakes of magnitude M 6.0

or greater have occurred within 50 miles (80 kilometers) of the proposed Project alignment (CGS, 2006). The

M 5.9 Whittier Narrows earthquake of 1987 is also included in the table because it was a significantly damaging

earthquake within 50 miles of the Project alignment. Also included in the table is the 1857 Fort Tejon

Earthquake. The location of this earthquake is uncertain due to lack of seismic instrumentation at the time and

due to the widespread damage and long rupture length; however, this very large earthquake produced surface

rupture on the local strands of the San Andreas Fault. A summary of each of these eight earthquake events is

presented in Table C.5-5.

Seven aftershocks measuring greater than M6.0 of larger earthquakes have also occurred within 50 miles of the

Project alignment, but are not included in the table. An additional 26 earthquakes with magnitudes between M

5.5 and M 6.0 that occurred between 1800 and 1999 are located within 50 miles of the Project alignment,

including numerous aftershocks of larger earthquakes. Figure C.5-2 shows locations of historic earthquakes in

the Project area and surrounding region.

Fault Rupture

Perhaps the most important single factor to be considered in the seismic design of electric transmission lines and

underground cables crossing active faults is the amount and type of potential ground surface displacement.

Two active and one potentially active faults cross the Project alignment, the San Andreas and San Gabriel Faults

and the Clearwater Fault, respectively. Both the San Andreas and San Gabriel Faults are mapped as Earthquake

Fault Zones6 in the vicinity of the Project alignment crossing. Although the Project will not be subject to the

regulations and guidelines related to the Alquist-Priolo Special Studies Zones Act because there will be no

6 The Alquist-Priolo Special Studies Zones Act, passed in 1972, requires the establishment of “Earthquake Fault Zones” (formerly

known as “special studies zones”) along known active faults in California. In order to be designated as an “Earthquake Fault Zone” a fault must be “sufficiently active and well defined” according to State guidelines. Development of occupied structures within these zones is regulated and must conform to strict building restrictions and codes, which are enforced to reduce the potential for damage and loss of life due to fault displacement.



Table C.5-5. Significant Historic Earthquakes

Date Approximate Distance (miles)

Earthquake Magnitude1

Name, Location, or Region Affected

Comments2

December 8, 1812 43.1 7.5? Wrightwood Earthquake

Caused collapse of Mission at San Juan Capistrano resulting in the death of 40 people.

July 11, 1855 18.7 6.0 Los Angles Region The bells at San Gabriel Mission Church were thrown down and twenty-six buildings in Los Angeles were damaged.

January 9, 1857

Unknown, currently assumed in the San Luis Obispo area.

Estimated from 7.9 to 8.25

Fort Tejon Earthquake

One of the largest earthquakes ever reported in the US. This earthquake caused damage from Monterey to San Bernardino and caused a surface rupture of greater than 220 miles in length. Due to sparse population of the time in it only resulted in 2 deaths. Average displacement along the fault was 15 feet, with a maximum displacement of 30 feet in the Carrizo Plain area.

January 16, 1857 34.0 6.3 Generally felt in the Los Angeles Region

Aftershock of the January 9, 1857 M7.9 Fort Tejon Earthquake.

July 29, 1894 48.1 6.2 Lytle Creek region Felt from Bakersfield to San Diego. Minor damage in the Mojave and Los Angeles areas.

July 21,1952 45.3 7.3 Kern County Earthquake

Resulted in the death of 12 people and $60 million in property Damage.

February 9, 1971 6.6 6.6 San Fernando

(Sylmar) Earthquake

This earthquake caused over $500 million in damage and resulted in 65 deaths. As A result of the damage from this earthquake, building codes were strengthened and the Alquist Priolo Special Studies Zone Act of 1972 was passed.

October 1, 1987 36.3 5.9 Whittier Narrows Earthquake

Resulted in eight deaths and $358 million in property damage. This earthquake occurred on a previously unknown blind thrust fault, the Puente Hills Fault.

January 17,1994 16.0 6.7 Northridge Earthquake

Resulted in 60 deaths and approximately $15 billion in property damage. Damage was significant and widespread, including collapsed freeway overpasses and more than 40,000 damaged buildings in Los Angeles, Ventura, Orange, and San Bernardino Counties.

Notes: 1) Earthquake magnitudes and locations before 1932 are estimated by Toppozada and others (1978, 1981, and 1982) based on reports of damage and felt effects.

2) Earthquake damage information compiled from the Southern California Data Center (SCEDC, 2005a and 2005b) and National Earthquake Information Center (NEIC, 2005) websites.

occupied structures constructed in the Earthquake Fault Zones as part of this Project, the presence of these

mapped zones indicates significant potential for fault rupture in the areas the Project crosses the “zones”. The

limits of these zones in the vicinity of the Project alignment fault crossings are presented on Figure C.5-3.

Fault rupture has occurred historically within the Project area. The 1857 Fort Tejon Earthquake caused rupture

of the local strands of the San Andreas Fault. Although future earthquakes could occur anywhere along the

length of the San Andreas and San Gabriel Faults, only regional strike-slip earthquakes of magnitude 6.0 or

greater are likely to be associated with surface fault rupture and offset (CGS, 1996). It is also important to note

that earthquake activity from unmapped subsurface faults is a possibility that is currently not predictable.



Liquefaction

Liquefaction is the phenomenon in which saturated granular sediments temporarily lose their shear strength

during periods of earthquake induced, strong groundshaking. The susceptibility of a site to liquefaction is a

function of the depth, density, and water content of the granular sediments and the magnitude and frequency of

earthquakes in the surrounding region. Saturated, unconsolidated silts, sands, and silty sands within 50 feet of

the ground surface are most susceptible to liquefaction. Liquefaction related phenomena include lateral

spreading, ground oscillation, flow failures, loss of bearing strength, subsidence, and buoyancy effects (Youd,

1978). In addition, densification of the soil resulting in vertical settlement of the ground can also occur.

In order to determine liquefaction susceptibility of a region, three major factors must be analyzed. These

include: (a) the density and textural characteristics of the alluvial sediments; (b) the intensity and duration of

groundshaking; and (c) the depth to groundwater. Surface materials beneath the proposed alignment meet the

criteria for liquefaction in the young alluvial deposits in the Santa Clara River valley, the Leona Valley, and in

the alluvial and creek deposits of intervening drainages. Older and finer or coarser grained, indurated, and/or

well-drained materials are less susceptible to liquefaction.

Seismic hazard mapping, delineating areas of potential liquefaction and seismically induced landslides, has been

conducted by the State of California for four of the 7.5-Minute Quadrangles that the Project alignment

traverses, the Del Sur, Sleepy Valley, Mint Canyon, and Newhall Quadrangles (CGS, 1998a, 1998b, 1999,

2003b, 2004). The Project alignment traverses mapped liquefaction hazard zones on the Del Sur, Mint Canyon,

and Newhall Quadrangles.

Seismic Slope Instability

Other forms of seismically induced ground failures which may affect the Project area include ground cracking

and seismically induced landslides. Landslides triggered by earthquakes have been a significant cause of

earthquake damage, in southern California large earthquakes such as the 1971 San Fernando and 1994

Northridge earthquakes triggered landslides that were responsible for destroying or damaging numerous

structures, blocking major transportation corridors, and damaging life-line infrastructure. Areas that are most

susceptible to earthquake-induced landslides are steep slopes in poorly cemented or highly fractured rocks, areas

underlain by loose, weak soils, and areas on or adjacent to existing landslide deposits. Local geologic units,

such as the Pelona Schist, and Mint Canyon, Castaic, and Saugus Formations, that are prone to landslides with

moderate to steep slopes, and previously existing landslides, both mapped and unmapped, are particularly

susceptible to this type of ground failure. The proposed Project route crosses areas mapped as areas of potential

earthquake-induced landslides on the CGS seismic hazard maps for the four mapped quadrangles along the

alignment (CGS 1998a, 1998b, 1999, 2003b, 2004).

C.5.1.4 Paleontology

Determination of the “significance” of a fossil can only occur after a fossil has been found and identified by a

qualified paleontologist. Until then, the actual significance is unknown. However, fossils are considered to be

scientifically significant if they meet or potentially meet any one or more of the following criteria:

• Taxonomy – fossils that are scientifically judged to be important for representing rare or unknown taxa, such as defining a new species.

• Evolution – fossils that are scientifically judged to represent important stages or links in evolutionary relationships, or fill gaps or enhance under-represented intervals in the stratigraphic record.

• Biostratigraphy – fossils that are scientifically judged to be important for determining or constraining relative geologic (stratigraphic) age, or for use in regional to interregional stratigraphic correlation problems.



• Paleoecology – fossils that are scientifically judged to be important for reconstructing ancient organism community structure and interpretation of ancient sedimentary environments.

• Taphonomy – fossils that are scientifically judged to be exceptionally well or unusually or uniquely preserved, or are relatively rare in the stratigraphy.

The most useful designation for paleontological resources in an EIR document is the “sensitivity” of a particular

geologic unit. Sensitivity refers to the likelihood of finding significant fossils within a geologic unit. The

following levels of sensitivity recognize the important relationship between fossils and the geologic formations

within which they are preserved.

• High Sensitivity. High sensitivity is assigned to geologic formations known to contain paleontological localities with rare, well-preserved, and/or critical fossil materials for stratigraphic or paleoenvironmental interpretation,

and fossils providing important information about the paleobiology and evolutionary history (phylogeny) of animal

and plant groups. Generally speaking, highly sensitive formations are known to produce vertebrate fossil remains

or are considered to have the potential to produce such remains.

• Moderate Sensitivity. Moderate sensitivity is assigned to geologic formations known to contain paleontological localities with moderately preserved, common elsewhere, or stratigraphically long-ranging fossil material. The

moderate sensitivity category is also applied to geologic formations that are judged to have a strong, but unproven

potential for producing important fossil remains (e.g., Pre-Holocene sedimentary rock units representing low to

moderate energy, of marine to non-marine depositional settings).

• Low Sensitivity. Low sensitivity is assigned to geologic formations that, based on their relative youthful age and/or high-energy depositional history, are judged unlikely to produce important fossil remains. Typically, low

sensitivity formations may produce invertebrate fossil remains in low abundance.

• Marginal Sensitivity. Marginal sensitivity is assigned to geologic formations that are composed either of pyroclastic volcanic rocks or metasedimentary rocks, but which nevertheless have a limited probability for

producing fossil remains from certain sedimentary lithologies at localized outcrops.

• Zero Sensitivity. Zero sensitivity is assigned to geologic formations that are entirely plutonic (volcanic rocks formed beneath the earth’s surface) in origin and therefore have no potential for producing fossil remains.

Significant California fossils are typically vertebrate fossils of late Quaternary and Tertiary age. The age of the

geologic units, their terrestrial origin, and the discovery of vertebrates in late Quaternary and Tertiary-aged

units in the region indicates that there is a likelihood that significant fossils may be found during excavation for

new tower footings in locations along the Project route. The most likely locations would be where towers are

placed on ridge tops and mesas capped by sandstone, siltstone or conglomerate (Lillegraven, 1973). Locations

where metamorphic or crystalline rocks occur have no potential for paleontological resources (Zero sensitivity).

Vertebrate fossils are known to occur in the late Quaternary and Tertiary sediments in the Project area, and the

project alignment crosses formations with known fossil localities. A paleontologic survey for the Antelope

Transmission Project was conducted for SCE by Dr. Grant Hurlburt, PhD (2004) from the California State

University at Stanislaus, and is summarized below.

This study and additional internet research indicates that moderately to highly sensitive formations occur along

the alignment. These units include the Anaverde Formation, the San Francisquito Formation, the Mint Canyon

Formation, the Castaic Formation, and the Saugus Formation. Significant vertebrate fossils may also be present

in older Quaternary alluvial deposits located below and on the eastern slopes of Portal Ridge; vertebrate fossils

could include horse, mammoth, gopher snake, kingsnake, leopard lizard, cottontail rabbit, pocket mouse,

kangaroo rat, and pocket gopher. Geologic units consisting of igneous (granitic rocks) and metamorphic rocks

(Pelona Schist) will not contain fossils and thus have zero sensitivity.

The proposed Project alignment crosses a small area of the Pliocene Anaverde Formation in the San Andreas

Rift zone; the SCE study indicates that this unit could contain significant fossils and internet research reveals

that the Anaverde Formation is known to contain plant fossils (UCMP website, 2006) resulting in a moderate to



high sensitivity for this unit. Between the Clearwater and San Francisquito faults (MPs 9.4 to 10.5) the

alignment crosses the San Francisquito Formation, which although there are no known localities in the project

vicinity, is known to contain vertebrate fossils, plesiosaur (UCMP website, 2006). Other fossils that could be

encountered in the San Francisquito Formation include turtles and other reptiles, birds, and early mammals that

were washed into the marine sediments (Hurlburt, 20046).

The alignment crosses approximately 2.3 miles of the middle Miocene Mint Canyon Formation (MPs 17.5 to

19.8) which is known to contain fossil localities in the project area, although no know localities lie along the

alignment. Significant fossils that could be encountered in the Mint canyon Formation include those of turtles,

rabbits, dogs, pronghorn antelope, camel, and three genera of fossil horses (Hurlburt, 20046). From

approximately MP 19.8 to 20.5, the proposed transmission line alignment crosses the middle to late Miocene

Castaic Formation which has two known fossil localities nearby; one with a fossil camel and the second with a

rare fossil tapir specimen (Hurlburt, 20046). The Plio-Pleistocene Saugus Formation is widespread beneath the

project route, from approximately MPs 20.6 to 22.8, 24.1 to 25.1, and 25.2 to 25.3 (total of approximately 3.3

miles), and is known to contain numerous fossil localities, although few are within the project area and none are

along the alignment. Significant fossils that may be encountered in the Saugus Formation include dogs and

horses.

C.5.2 Regulatory Framework

Geologic resources and geotechnical hazards are governed primarily by local jurisdictions. The conservation

elements and seismic safety elements of city and county general plans contain policies for the protection of

geologic features and avoidance of hazards, but do not specifically address transmission line construction

projects.

The two major environmental statutes that guide the design and construction of new transmission lines are

NEPA and CEQA. These statutes set forth a specific process of environmental impact analysis and public

review. In addition, the project owner must comply with several additional federal, state and local applicable

statutes, regulations and policies. Relevant, and potentially relevant, statutes, regulations and policies are

discussed below.

C.5.2.1 Federal

Geology and Mineral Resources

Protection of Geologic and Mineral Resources: National Environmental Policy Act (NEPA), as amended, 42

U.S.C. 4321, et seq., 40 C.F.R. Parts 1500-1508.

Regulations promulgated under 36 CFR 228 state that each District Ranger has jurisdiction over prospecting and

mining operations on Forest Service lands, including permitting, approval of operation plans, and periodic

inspection of mining facilities. It is the purpose of the regulations to set forth rules and procedures through

which use of the surface of National Forest System lands in connection with operations authorized by the United

States mining laws (30 U.S.C. 21–54), which confer a statutory right to enter upon the public lands to search

for minerals, shall be conducted so as to minimize adverse environmental impacts on National Forest System

surface resources.

Forest Service Manual (FSM) 2800 of the National Forest Service provides policy, management objectives, and

regulations for Minerals and Geologic Resources. FSM 2800 consists of several chapters, each providing policy

and regulation for a different aspect of mineral or geologic resource management, as follows: 2810 - Mining



Claims; 2820 - Mineral Leases, Permits, and Licenses; 2830 - Mineral Reservations and Rights Outstanding;

2840 – Reclamation; 2850 - Mineral Materials; 2860 - Forest Service Authorized Prospecting and Minerals

Collecting; and 2880 - Geologic Resources, Hazards, and Services.

Paleontology

Protection of Paleontological Resources: National Environmental Policy Act (NEPA), as amended, 42 U.S.C.

4321, et seq., 40 C.F.R. Parts 1500-1508.

The Forest Service issues permits authorizing both project-related identification and mitigation efforts in

addition to research related investigations based on the provisions of the Federal Land Policy and Management

Act of 1976 (FLPMA) (43 USC 1701 1782) and the Antiquities Act of 1906. Regulations promulgated under 36

CFR 261 state that each Regional Forester has jurisdiction over “Protection of objects or places of historical,

archaeological, geological or paleontological interest” (36 CFR 261.70(a)(5)), and that the following are

prohibited: “Excavating, damaging, or removing any vertebrate fossil or removing any paleontological resource

for commercial purposes without a special use permit” (36 CFR 261.9 (g)). FSM Chapter 2880 - Geologic

Resources, Hazards, and Services contains policies and regulations related to paleontologic resource

management and preservation. Forest Service policy makes the salvage of known paleontological resources a

standard condition of their Special Use Permits. Treatment standards are specific to each forest and rely heavily

upon implementation of a mitigation plan developed under the auspices of professional paleontologists at

regional museums and universities.

C.5.2.2 State

Geologic and Seismic Hazards

California Environmental Quality Act (CEQA) (Pub. Resource Code sections 21000-21177.1). CEQA was

adopted in 1970 and applies to most public agency decisions to carry out, authorize or approve projects that

may have adverse environmental impacts. CEQA requires that agencies inform themselves about the

environmental effects of their proposed actions, consider all relevant information, provide the public an

opportunity to comment on the environmental issues, and avoid or reduce potential environmental harm

whenever feasible. Relevant CEQA sections include those for protection of geological and mineral resources,

protection of soil from erosion.

The Alquist-Priolo Earthquake Fault Zoning Act of 1972 (formerly the Special Studies Zoning Act) regulates

development and construction of buildings intended for human occupancy to avoid the hazard of surface fault

rupture. While this Act does not specifically regulate overhead transmission lines, it does help define areas

where fault rupture is most likely to occur. This Act groups faults into categories of active, potentially active,

and inactive. Historic and Holocene age faults are considered active, late Quaternary and Quaternary age faults

are considered potentially active, and pre-Quaternary age faults are considered inactive. These classifications

are qualified by the conditions that a fault must be shown to be “sufficiently active” and “well defined” by

detailed site-specific geologic explorations in order to determine whether building setbacks should be

established.

The Seismic Hazards Mapping Act (the Act) of 1990 (Public Resources Code, Chapter7.8, Division 2) directs

the California Department of Conservation , Division of Mines and Geology [now called California Geological

Survey (CGS)] to delineate Seismic Hazard Zones. The purpose of the Act is to reduce the threat to public

health and safety and to minimize the loss of life and property by identifying and mitigating seismic hazards.

Cities, counties, and state agencies are directed to use seismic hazard zone maps developed by CGS in their



land-use planning and permitting processes. The Act requires that site-specific geotechnical investigations be

performed prior to permitting most urban development projects within seismic hazard zones.

The California Building Code (CBC, 2001) is based on the 1997 Uniform Building Code, with the addition of

more extensive structural seismic provisions. Chapter 16 of the CBC contains definitions of seismic sources and

the procedure used to calculate seismic forces on structures. As the proposed Project route lies within UBC

Seismic Zone 34, provisions for design should follow the requirements of Chapter 16. Chapter 33 of the CBC

contains requirements relevant to the construction of underground transmission lines.

Paleontology

Protection of paleontological resources (certain fossils found in sedimentary rocks) in included in the Cultural

Resources section of CEQA.

C.5.2.3 Local

The safety elements of General Plans for the cities and the County along the proposed alignment contain policies

for the avoidance of geologic hazards and/or the protection of unique geologic features. A survey of General

Plans along the proposed alignment indicated that most municipalities require submittal of construction and

operational safety plans for proposed construction in areas of identified geologic and seismic hazards for review

and approval prior to issuance of permits. County and local grading ordinances establish detailed procedures for

excavation and grading required for underground construction.

C.5.3 Significance Criteria

A wide range of potential impacts, including loss of mineral and paleontological resources, slope instability

including landslides, debris flows and slope creep, and seismic hazards including surface fault rupture, strong

groundshaking, liquefaction, and seismically induced landslides, was considered in this analysis. Each of these

potential geologic, soils, and paleontologic impacts is discussed in the following sections.

Geology and Soils

Geologic conditions were evaluated with respect to the impacts the Project may have on the local geology, as

well as the impact that specific geologic hazards may have upon the transmission line and its related facilities.

The significance of these impacts was determined on the basis of National Environmental Policy Act (NEPA)

and CEQA statutes, guidelines and appendices, thresholds of significance developed by local agencies,

government codes and ordinances, and requirements stipulated by California Alquist-Priolo statutes.

Significance criteria and methods of analysis were also based on standards set or expected by agencies for the

evaluation of geologic hazards.

Impacts of the Project on the geologic environment would be considered significant and require additional

mitigation if Project construction or operation would result in any of the following criteria being met:

• Criterion GEO1: Unique geologic features or geologic features of unusual scientific value for study or interpretation would be disturbed or otherwise adversely affected by the proposed new

transmission line towers and the associated construction activities.

• Criterion GEO2: Known mineral and/or energy resources would be rendered inaccessible by transmission line construction.

• Criterion GEO3: Geologic processes, such as landslides or erosion, could be triggered or accelerated by construction or disturbance of landforms.



• Criterion GEO4: Substantial alteration of topography would be required or could occur beyond that which would result from natural erosion and deposition.

• Criterion GEO5: High potential for earthquake-related ground rupture in the vicinity of major fault crossings along the transmission line route, resulting in probable damage to the transmission line

structures.

• Criterion GEO6: High potential for seismically induced landslides, liquefaction, settlement, lateral spreading and/or surface cracking at the substations or along the transmission line route, which will likely

cause damage to proposed Project structures.

• Criterion GEO7: Presence of corrosive soils or other unsuitable soils, which would likely damage the transmission line support structures, including the substation foundations.

• Criterion GEO8: Potential of possible landslides on existing unstable slopes to damage the transmission line support structures.

Paleontology

Determination of the “significance” of a fossil can only occur after a fossil has been found and identified by a

qualified paleontologist. Until then, the actual significance is unknown. The most useful designation for

paleontological resources in an EIR document is the “sensitivity” of a particular geologic unit. Sensitivity refers

to the likelihood of finding significant fossils within a geologic unit. Categories of “sensitivity” are defined in

Section C.5.1.4. Fossils are considered to be scientifically significant if they meet or potentially meet any one

or more of the following criteria:

• Taxonomy – fossils that are scientifically judged to be important for representing rare or unknown taxa, such as defining a new species

• Evolution – fossils that are scientifically judged to represent important stages or links in evolutionary relationships, or fill gaps or enhance under-represented intervals in the stratigraphic record

• Biostratigraphy – fossils that are scientifically judged to be important for determining or constraining relative geologic (stratigraphic) age, or for use in regional to interregional stratigraphic correlation problems

• Paleoecology – fossils that are scientifically judged to be important for reconstructing ancient organism community structure and interpretation of ancient sedimentary environments

• Taphonomy – fossils that are scientifically judged to be exceptionally well or unusually or uniquely preserved, or are relatively rare in the stratigraphy.

In southern California, generally fossils of land-dwelling vertebrates are considered the most significant.

Impacts of the Project on paleontology would be considered significant and require additional mitigation if

Project construction or operation would result in any of the following criteria being met:

• Criterion GEO9: Directly or indirectly destroy a unique paleontological resource.

C.5.4 Applicant-Proposed Measures

The following are Applicant-Proposed Measures (APMs) to reduce geological resource related impacts:

Table C.5-6. Applicant-Proposed Measures – Geology, Soils, and Paleontology

Measure Number SCE-Proposed Measure

Geology and Soils

APM GEO-1 For new substation construction (e.g., expansion of Antelope Substation), specific requirements for seismic design will be followed based on the Institute of Electrical and Electronic Engineers’ 693 “Recommended Practices for Seismic Design of Substation”.



Table C.5-6. Applicant-Proposed Measures – Geology, Soils, and Paleontology

Measure Number SCE-Proposed Measure

APM GEO-2 Prior to final design of substation facilities and transmission line tower foundations, a geotechnical study would be performed to identify site-specific geologic conditions in enough detail to support good engineering practice.

APM GEO-3 Transmission line and substation construction activities would be performed in accordance with the soil erosion/water quality protection measures specified in the Construction SWPPP.

Paleontology

APM PAL-1

The following mitigation measures have been developed to reduce the potential impacts of project construction on paleontological resources to a less than significant level. The measures are derived from the guidelines of the SVP and meet the requirements of Kern and Los Angeles counties and CEQA. These mitigation measures have been used throughout California and have been demonstrated to be successful in protecting paleontological resources while allowing timely completion of construction:

• A certified paleontologist would be retained by SCE to supervise monitoring of construction excavations and to produce a mitigation plan for the proposed Project. Paleontological monitoring would include inspection of exposed rock units and microscopic examination of matrix to determine if fossils are present. The monitor would have authority to temporarily divert grading away from exposed fossils in order to recover the fossil specimens.

• If microfossils are present, the monitor would collect matrix for processing. In order to expedite removal of fossiliferous matrix, the monitor may request heavy machinery to assist in moving large quantities of matrix out of the path of construction to designated stockpile areas. Testing of stockpiles would consist of screen washing small samples to determine if significant fossils are present. Productive tests would result in screen washing of additional matrix from the stockpiles to a maximum of 6,000 pounds per locality to ensure recovery of a scientifically significant sample.

• Quaternary Alluvium, Colluvium, and Quaternary Landslide Deposits have a low paleontological sensitivity level, and would be spot-checked on a periodic basis to insure that older underlying sediments are not being penetrated.

• A certified paleontologist would prepare monthly progress reports to be filed with the client. • Recovered fossils would be prepared to the point of curation, identified by qualified experts, listed in a

database to allow analysis, and deposited in a designated repository.

• At each fossil locality, field data forms would record the locality, stratigraphic columns would be measured, and appropriate scientific samples submitted for analysis.

• The certified paleontologist would prepare a final mitigation report to be filed with the client, the lead agency, and the repository.

C.5.5 Impact Analysis: Proposed Project/Action

The geologic, seismic, and paleontologic impacts of the proposed Project are discussed below under

subheadings corresponding to each of the significance criterion presented in the preceding section. The analysis

describes the impacts of the proposed Project related to geologic and seismic hazards, mineral resources, and

paleontology and, for each criterion, determines whether implementation of the proposed Project would result in

significant impacts.

Unique Geologic Features (Criterion GEO1)

No unique geologic features or geologic features of unusual scientific value for study or interpretation would be

disturbed or otherwise adversely affected by the proposed Project. No impact would occur.

Known Mineral and/or Energy Resources (Criterion GEO2)

Although known sand and gravel resources, and a decorative stone quarry are located within the general Project

area, none of the Project facilities are located within an active production area. Therefore, construction and

operation of the Project is not expected to interfere with access to these resources. The access road for the



Bouquet Canyon Stone Company Quarry is located near the proposed Project along Del Sur Ridge. The quarry

uses Del Sur Ridge Road for transportation of its product from the quarry. However, use of this road by

construction traffic for the Project would not affect the ability of the quarry to transport their product. No

impact would occur.

The Project alignment does cross the southeast corner of the Southeast Area of the Honor Rancho oil and gas

field, but is not located near any active wells. However, this area is only operated as a natural gas storage

reservoir by SoCalGas and is not expected to generate any additional gas resources other than the amount

injected for storage. Therefore, construction and operation of the Project is not expected to interfere in access to

or operation of the gas reservoir. No impact would occur would occur.

Landslides or Erosion Triggered or Accelerated by Construction (Criterion GEO3)

Impact G-1: Excavation and grading during construction activities could cause slope instability.

Destabilization of natural or constructed slopes could occur as a result of construction activities due to

excavation and/or grading operations. Many of the hills and slopes crossed by the Project alignment are

underlain by geologic units prone to landslides, including the Pelona Schist, the Mint Canyon Formation, the

Castaic Formation, and the Saugus Formation. Unmapped landslides and areas of localized slope instability may

be encountered.Excavation operations associated with tower foundation construction and grading operations for

temporary and permanent access roads and work areas could result in slope instability, resulting in landslides,

slumps, soil creep, or debris flows. Slope failures are more likely to occur in areas with a history of previous

failure, in weak geologic units exposed on unfavorable slopes and areas of weak, and in areas of fault-sheared

rock. Many of the hills and slopes crossed by the Project alignment are underlain by geologic units prone to

landslides, including the Pelona Schist, the Mint Canyon Formation, the Castaic Formation, and the Saugus

Formation. Unmapped landslides and areas of localized slope instability may be encountered. Instances of

triggered slope failure could cause damage to nearby properties and roads, Project facilities and construction

equipment, and could potentially result in injury to workers or the public. Prior to final design of substation

facilities and transmission line tower foundations, SCE plans to perform geotechnical studies to identify site-

specific geologic conditions (APM GEO-2). Mitigation Measure G-1 (Protect Against Slope Instability), which

adds specific requirements to the planned geotechnical investigations prior to final Project design, ensures that

potential impacts would be reduced to less-than-significant levels (Class II).

Mitigation Measure for Impact G-1

G-1 Protect Against Slope Instability. Design-level geotechnical investigations performed by the

Applicant shall be performed by a licensed geologist or engineer and shall include evaluation of slope

stability issues in areas of planned grading and excavation, and provide recommendations for

development of grading and excavation plans. Based on the results of the geotechnical investigations,

appropriate support and protection measures shall be designed and implemented to maintain the

stability of slopes adjacent to newly graded or regraded access roads and work areas during and after

construction. These measures shall include, but are not limited to, retaining walls, visqueen, removal

of unstable materials, and avoidance of highly unstable areas. SCE shall document compliance with

this measure prior to the start of construction by submitting a report to the CPUC and Forest Service

AFS (for areas on NFS land) for review and approval. The report shall document the investigations

and detail the specific support and protection measures that will be implemented.



Impact G-2: Erosion could be triggered or accelerated by construction or disturbance of landforms.

Excavation and grading for tower and substation foundations, work areas, and access roads could loosen soil or

remove stabilizing vegetation and expose areas of loose soil. These areas, if not properly stabilized during

construction, could be subject to increased soil loss and erosion by wind and stormwater runoff. Newly

constructed and compacted engineered slopes can also undergo substantial erosion through dispersed sheet flow

runoff. More concentrated runoff can result in the formation of small erosional channels and larger gullies, each

compromising the integrity of the slope and resulting in significant soil loss. Portions of the Project alignments

cross areas underlain by soils classified as having moderate to severe hazard of erosion on roads and trails. SCE

has committed to perform transmission line and substation construction activities in accordance with the soil

erosion/water quality protection measures specified in the Construction SWPPP (APM GEO-3). Implementation

of Mitigation Measure G-2 (Minimization of Soil Erosion) ensures that potential impacts from erosion related to

grading and use of access roads and work areas in areas of moderate to severe erosion potential during

construction would be reduced to less-than-significant levels (Class II). Furthermore, Application of Mitigation

Measure V-4a (Construct, Operate, and Maintain with Helicopters - see Section C.15, Visual Resources) would

reduce the number of miles of access and spur roads that would be constructed or improved on NFS lands and

would therefore reduce the amount of potential erosion.


G-2 Minimization of Soil Erosion. The Construction SWPPP for the Project shall include BMPs

designed to minimize soil erosion along access roads and at work areas. Appropriate BMPs may

include construction of water bars, grading road surfaces to direct flow away from natural slopes, use

of soil stabilizers, and consistent maintenance of roads and culverts to maintain appropriate flow

paths. Silt fences and straw bales installed during construction shall be removed to restore natural

drainage during the cleanup and restoration phase of the project. Where access roads cross streams or

drainages, they shall be built at or close to right angles to the streambeds and washes and culverts or

rock crossings shall be used to cross streambeds and washes. Design of appropriate BMPs should be

conducted by or under the direction of a qualified geologist or engineer.

Substantial Alteration of Topography (Criterion GEO4)

Impact G-3: Minor changes in topography due to excavation and grading.

Only limited shallow grading for access roads and work areas is anticipated and excavations are limited to the

tower footing areas and within the substations for foundations. Therefore, substantial alteration7 of the

topography is not anticipated, however minor changes to topography would occur. The minor changes in

topography anticipated due to grading of work areas and new access roads would be less than significant

without mitigation (Class III). However, the implementation of Mitigation Measures G-2 (Minimization of Soil

Erosion) during construction and B-1a (Provide Restoration/Compensation for Impacts to Native Vegetation

Communities) following construction would substantially reduce the effects of minor changes in topography due

to grading for the Project.

7 Substantial alteration of topography are changes in the character of the topography (slope and gradient) due to grading,

excavation, or cut and fill that result in increased wind or water erosion due to resultant drainage pattern changes.



Earthquake-Related Ground Rupture (Criterion GEO5)

Impact G-4: Transmission line damaged by surface fault ruptures at crossings of active faults.

Project facilities would be subject to hazards of surface fault rupture at crossings of active traces of the San

Andreas Fault between Miles 3.8 and 5.1 and of the San Gabriel Fault at approximately Mile 25.1 along the

proposed alignment. Both of these faults are significant active faults with mapped Alquist-Priolo zones, as

shown in Figure C.5-3, capable of multiple feet of offset. Hazards would not be as great where the proposed

alignment crosses the trace of the potentially active Clearwater Fault at approximately Mile 9.4, shown on

Figure C.5-2, which is only likely to generate small to moderate earthquakes with minor rupture or have minor

triggered fault rupture in the event of a large local earthquake on the San Andreas or San Gabriel faults. Fault

crossings where multiple feet of displacement are expected along active faults are best crossed as overhead lines

with towers placed well outside the fault zone to allow for the flex in the cables to absorb offset. In addition to

the geotechnical study required by APM GEO-2, Mitigation Measure G-4 (Minimize Project Structures Within

Active Fault Zone) shall be completed prior to final Project design for the San Andreas and San Gabriel fault

crossings to minimize the length of transmission line within fault zones. Impacts associated with overhead active

fault crossings can be mitigated to less-than-significant levels (Class II).


G-4 Minimize Project Structures Within Active Fault Zone. Perform a geologic/geotechnical study to

confirm location of mapped traces of active and potentially faults (the San Gabriel and San Andreas

Faults) crossed by the alignment. Any crossing of an active fault crossing (overhead or underground)

shall be made as close to perpendicular to the fault as possible to make the segment cross the shortest

distance within an active fault zone. Tower locations shall be adjusted as necessary to avoid placing

tower footings on or across mapped fault traces. Towers on either side of a fault shall be designed to

provide a significant amount of slack to allow for potential fault movement and ground surface

displacement.

Damage Related to Earthquake Induced Phenomena (Criterion GEO6)

Impact G-5: Project structures could be damaged by landslides, liquefaction, settlement, lateral spreading, and/or surface cracking resulting from seismic events.

There is a high potential for seismically induced landslides, liquefaction, settlement, lateral spreading and/or

surface cracking at the substations or along the transmission line route would likely cause damage to proposed

Project structures. Seismically induced ground failure includes liquefaction, lateral spreading, seismic slope

instability (landslide) and ground-cracking. Liquefaction occurs in low-lying areas where saturated noncohesive

sediments are found. Lateral spreading occurs along waterfronts or canals where non-cohesive soils could move

out along a free-face. Slope instability and ground-cracking can occur anywhere, however areas that are most

susceptible to earthquake-induced landslides are steep slopes in poorly cemented or highly fractured rocks, areas

underlain by loose, weak soils, and areas on or adjacent to existing landslide deposits.

Much of the Project alignment is located along hillsides or ridgelines in geologic units of moderate to steep

slopes, which are particularly susceptible to this type of ground failure. Some of these areas, which include the

Pelona Schist, and Mint Canyon, Castaic, and Saugus Formations, have a high possibility of seismic-induced

ground failure in the form of landsliding or ground-cracking. Portions of the alignment are located in areas

underlain by potentially liquefiable alluvial deposits and may be subject to liquefaction related phenomena

during a seismic event, resulting in significant impact. Potentially liquefiable deposits include the young alluvial



deposits in the Santa Clara River valley, the Leona Valley, and in the alluvial and creek deposits of intervening

drainages. Prior to final design of substation facilities and transmission line tower foundations, SCE plans to

perform geotechnical studies to identify site-specific geologic conditions (APM GEO-2). Implementation of

Mitigation Measure G-5 (Geotechnical Investigations for Liquefaction and Slope Instability) below would add

specific requirements to the planned geotechnical investigations prior to final Project design and would reduce

potentially significant impacts for all potential instances of seismically related ground failure along the Project

route to less-than-significant levels (Class II).


G-5 Geotechnical Investigations for Liquefaction and Slope Instability. Since seismically induced

ground failure has the potential to damage or destroy Project components, the Applicant shall perform

design-level geotechnical investigations specifically to assess the potential for liquefaction, lateral

spreading, seismic slope instability, and ground-cracking hazards to affect the approved Project and

all associated facilities. Where these hazards are found to exist, appropriate engineering design and

construction measures shall be incorporated into the Project designs. Such measures could include

construction of pile foundations, ground improvement of liquefiable zones, installation of flexible bus

connections, and incorporation of slack in cables to allow ground deformations without damage to

structures.

Impact G-6: Project structures could be damaged by strong groundshaking.

Severe groundshaking should be expected in the event of an earthquake on the faults in the Project area. The

alignment would also be subject to groundshaking from any of the major faults in the region. While the shaking

would be less severe from an earthquake that originates farther from the alignment, the effects, particularly on

the ridgelines, could be damaging to Project structures, a significant impact. It is likely that the Project facilities

would be subjected to at least one moderate or larger earthquake occurring close enough to produce strong

groundshaking in the Project area. SCE plans to perform geotechnical studies to identify site-specific geologic

conditions prior t

C.5 Geology, Soils, and Paleontology...Andreas Fault Zone are several members of the Anaverde...

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